This invention relates to driveline torsion isolator mechanisms operable over the entire operational range of a driveline. More specifically, the invention relates to such mechanisms for vehicle drivelines.
It is well-known that the speed of an Otto or Diesel cycle engine output or crankshaft varies even during so-called steady-state operation of the engine, i.e., the shaft continuously accelerates and decelerates about the average speed of the shaft. The accelerations and decelerations are, of course for the most part, a result of power pulses from the engine cylinders. The pulses may be of uniform frequency and amplitude when cylinder charge density, air/fuel ratio, and ignition are uniform. However, such uniformity does not always occur, thereby producing pulses which vary substantially in frequency and amplitude. Whether uniform or not, the pulses, which are herein referred to as torsionals, are transmitted through vehicle drivelines and to passengers in vehicles. The torsionals, which manifest themselves as vibrations, are detrimental to drivelines and derogate passenger-ride quality. Further, when an engine is abruptly accelerated and/or decelerated by accelerator pedal movement or other factors, torque pulses ring through the driveline and also derogate ride quality, such pulses are herein also referred to as torsionals.
Since the inception of the automobile, many torsion damping devices or schemes have been proposed and used to isolate and dampen driveline torsionals. For example, master clutches, used in combination with mechanical transmissions, have long employed springs and secondary mechanical friction devices to respectively isolate and dampen torsionals. Typically, torsionals are isolated or absorbed by a plurality of circumferentially spaced, coil springs disposed in parallel with each other between the master clutch primary friction input and splined output. Damping is provided by secondary mechanical friction surfaces disposed in parallel with the springs and biased together with a predetermined force. Damping occurs when the amplitude of the torsionals exceeds the breakaway or slip torque of the secondary friction surfaces. With this arrangement, portions of the torsionals less than the slip torque of the secondary friction surfaces are transmitted directly through the clutch without flexing or isolation by the springs, i.e., the arrangement provides neither torsion isolation nor damping. If the slip torque of the secondary friction surfaces is reduced by design or wear of the secondary surfaces, damping is reduced. Further, any portions of the torsionals greater than the spring energy absorption or storage capacity are also transmitted directly through the clutch. If the spring rate is increased to prevent spring collapse, the springs transmit lesser amplitude torsionals directly through with little or no effective isolation or absorption of the torsionals.
To increase the operational spring range and storage capacity of a torsion damping assembly, Wemp in U.S. Pat. No. 1,978,922, proposed using a low spring rate torsion sleeve capable of flexing substantially more than the coil springs used with master clutches. This arrangement, like the master clutch arrangement, also employs secondary mechanical friction surfaces disposed in parallel and biased together with a predetermined force to provide damping. Hence, the Wemp arrangement also fails to provide isolation and damping of torsionals below the slip or breakaway torque of the secondary friction surfaces. The Wemp arrangement is also underdamped if the slip or breakaway torque of the secondary friction surfaces is reduced.
It is known to dampen driveline torsionals with a vane damper as may be seen by reference to U.S. Pat. No. 4,690,256 to Bopp et al and incorporated herein by reference. In U.S. Pat. No. 4,690,256 there is disclosed a torsion damping isolator assembly immersed in the oil of a torque converter housing. The assembly includes resilient means for transmitting driveline torque between input and output drives, and an expandable chamber mechanism connected in parallel with the resilient means. The resilient means are of the long travel type allowing about fifty rotational degrees of travel between the input and output drives. The mechanism, which is also of the long travel type, includes first and second relatively movable members connected to opposite ends of the resilient means and defining at least two chambers which vary inversely in volume in response to flexing of the resilient means and which are in communication with the torque converter oil via restricted passages. The restricted passages provide inflow or charging of the volumes with torque converter oil to prevent cavitation and control damping by restricting the rate of outflow of oil from the volumes.
The long travel resilient and expandable chamber mechanism of U.S. Pat. No. 4,690,256 has proven to be an excellent torsion damping assembly. However, problems have arisen with respect to life of the long travel resilient means, with respect to control of oil flow to and from the volumes of the expandable chamber mechanism for respectively preventing cavitation of the expanding volumes and for ensuring sufficient oil pressure building up in the contracting volumes, and with respect to manufacture of the mechanism at a low cost with necessary accuracy.